The invention relates to thermoplastic elastomers of high strength and elasticity and of good dyeability and polymer blends of high impact strength produced therefrom, which are suitable for use in the vehicle industry, in the domestic appliances industry and in medical technology. The invention also relates to a method for producing these thermoplastic elastomers.
Thermoplastic elastomers, such as styrene-butadiene block copolymers, thermoplastic polyurethanes, polyester amides, polyether amides, thermoplastic copolyester elastomers and polyolefin alloys with elastomers are known (Rader, C., Kunststoffe 83 (1993) 10, 777-781; Kunststoffe 86 (1996) 12, 1845-1851).
The special advantage of polyolefin alloys with elastomers as thermoplastic elastomers lies in the easy processability and the advantageous recycling properties of these products.
The material properties of thermoplastic elastomers based on polyolefin alloys with elastomers, such as strength and elasticity, are determined by the composition of the polyolefin component and the elastomeric component and the distribution of the elastomeric component in the polyolefin component (Moore, P., Polypropylene Handbook, Carl Hanser-Verlag, Munich 1996, 218-225).
Known elastomeric components for thermoplastic elastomers based on polypropylene are ethylene-propylene elastomers (EP 672 712; EP 614940), ethylene-propylene-diene elastomers (EP 547 843; EP 409542), ethylene-vinyl acetate copolymers (BE 899507; Coran, A., Rubber Chem. Technol. 54 (1981), 892), chlorosulfinated polyethylene (U.S. Pat. No. 4,141,878), elastomeric copolymers of ethylene and C.sub.4 -C.sub.8 olefins, such as elastomeric ethylene-butene copolymers, ethylene-hexene copolymers, ethylene-octene copolymers (Yamaguchi, M., J. Appl. Polymer Sci. 62 (1996), 87-97; 63 (1997), 467-474; Yu, T., J. Plastic Film & Sheeting 10 (1994) 1, 539-564), as well as elastomeric, atactic polypropylenes (EP 334 829) in amounts of 35 to 70% by weight, based on the polyolefin mixture.
Furthermore, the vulcanization of elastomeric components in polyolefin alloys based on polypropylene/ethylene-propylene-diene elastomers, by the addition of dodecyl mercaptan (DE 26 20 820), sulfur (EP 336780) or tetrabutylthiuram disulfide (EP 376 213) is known. However, these formulations have the disadvantage of a strong discoloration, so that semi-finished products and molded objects of these materials can be used only when dyed black.
Furthermore, for the preparation of thermoplastic elastomers by compounding polypropylene with ethylene-propylene-diene elastomers, the use of thermally decomposing free radical-forming agents, such as azo compounds (U.S. Pat. No. 5,079,283) or peroxides (U.S. Pat. No. 5,459,201; Kim, Y., Polymer Engn. Sci. 35 (1995) 20, 1592-1594; BE 841507) or of thermally decomposing free radical-forming agents in combination with divinyl compounds, such as divinylpyridine (J 88 067 802) or divinylbenzene (U.S. Pat. No. 4,912,148, EP 311451), is also known.
For formulations of polypropylenes and elastomeric ethylene-hexene copolymers, the modification of the blends by electron irradiation is known (JP 96 301 927).
Thermoplastic elastomers are also known as ternary blends of polyethylenes, polypropylenes and ethylene-propylene-diene elastomers (EP 699522; Kim, J. Applied Polymer Sci. 60 (1996), 2199-2206).
Thermoplastic elastomers of good dyeability and high elasticity can be achieved by means of these formulations. However, high strength requirements are not fulfilled.
Impact-resistant polymer blends of polyolefins and elastomers are known. Known impact-resistant components for polypropylene are amorphous ethylene-propylene-diene elastomers (Michaeli, W., Kunststoffberater (1990) 3, 38-43; Kloos, F., Angewandte Makromelekulare Chemie 185/186 (1991), 97-108), ethylene-propylene elastomers (Kim, B., J. Applied Polymer Sci. 60 (1996), 2207-2218, J. Applied Polymer Sci. 60 (1996), 1391-1403), also in the form of reactor blends of polypropylene and ethylene-propylene rubber (Kresge, E., Macromol. Symp. 53 (1992), 173-189, Schwager, H., Kunststoffe 82 (1992) 6, 499-501), butadiene-.alpha.-methylstyrene rubber (Natov, M., Plaste u. Kautschuk 38 (1991) 3, 85-88), styrene-butadiene block copolymers (Karger-Kocsis, J., Kunststoffe 74 (1984), 104-107), elastomeric copolymers of ethylene and higher molecular weight C.sub.4 -C.sub.8 olefins (Yu, T., ANTEC 94, 2439-2441; Meiske, L., ANTEC 96, 2001-2005) and elastomeric ethylene-vinyl acetate copolymers (Gupta, A., J. Applied Polymer Sci. 45 (1992), 1303-1312) in amounts of 10 to 35% by weight, based on the polyolefin mixture.
The limited compatibility of the impact-resistant components is a disadvantage of these unmodified blends.